Magnetic resonance elastography (MRE) combines magnetic resonance imaging (MRI) with sound waves to create a visual map, or elastogram, of the stiffness or elasticity of human tissue. The examining physician has traditionally evaluated “tissue stiffness” through palpation. This method is limited to organs that are superficial and is subject to the skill of the physician. MRE provides a means to: examine large anatomic regions at greater depths; quantify the stiffness allowing for cross-sectional comparison of disease severity and longitudinal comparison of an individual's disease progression or regression; and provide a 3D image of stiffness so the relationship to surrounding organs and vasculature can be incorporated into treatment (i.e. surgical or radiotherapeutic) planning. Currently, technology is being clinically applied to detect the hardening of the liver in order to diagnose diseases such as liver fibrosis and cirrhosis. Existing technology typically uses a flat passive acoustic driver to deliver low-frequency acoustic waves from an active driver to the patient. Flat passive acoustic drivers are adequate to vibrate a large and superficial liver, but have been found to be ineffective at penetrating through the entire human abdomen. In particular, flat passive acoustic drivers have difficulty detecting cancer and other disease states with high enough accuracy in small, deep organs including the kidneys, ovaries, and pancreas. MRE as a technology is less than 10 years old, and much of the previous development work has been focused in MRI pulse sequence development and image reconstruction algorithms. Very little attention has been devoted to the optimization of acoustic drivers.
There is a need for an improved acoustic passive driver design which will improve the stiffness images produced using MRE to broaden the number of clinical applications of this technology to detect cancer or other diseases in small, deep organs or in other portions of the patient's body